rendering 3D video/image for google cardboard
Found it!

Once you have set up your animation or single frame:

In your Scene tab enable Views and select Stero 3D



Select the Camera on the scene and go to the Camera tab. Sort out the interocular disctance this should be 0.06 = 6cm, the distance between your eyes. Set Lens to Panoramic



Go to the Render tab, change the Dimensions -> Resolution to be the resolution for a single eye (this will depend on the android phone you are using)



Again, in the Render tab scroll down to the Output and change the Views Format to be Stereo 3D. Set the Stereo Mode to be Side-by-Side.



Press Render or Animation depending on whether you are creating a single image or a video, and you should be done!

Check an example output here: https://youtu.be/fEFmGVymbUg (Which annoyingly youtube currently seems to be converting to different 3D formats!)

To render for VR, see this: http://b3d101.org/en/vr/